CHAPTER 5Shells Within Shells
This chapter discusses the relationship between the shell and the programs it calls, with a particular focus on subshells—additional shells run by a shell script in a new process. This chapter also discusses shell context and the distinction between shell variables and environment variables.
This chapter relies more heavily than previous chapters on a firm understanding of the UNIX process model. (While Windows does not use this model, UNIX-like shell environments running on Windows tend to emulate it at least some.) UNIX systems can run multiple programs at once. In fact, not only can multiple programs be running at once, but multiple instances of a single program also can be running at ...